The present invention relates to electrical transformers and particularly to transformers having amorphous metal cores.
The invention herein disclosed is based upon work sponsored in part by the Electric Power Research Institute, Palo Alto, Calif.
Traditionally, electrical transformer cores have been formed of high grain oriented silicon steel laminations. Over the years, significant improvements have been made in such electrical steels to permit reductions in transformer core sizes, manufacturing costs and the losses introduced into an electrical distribution system by the transformer core. As the cost of electrical energy continues to rise, reductions in core loss have become an increasingly important design consideration in all sizes of electrical transformers. For this reason, amorphous ferromagnetic materials are being used as transformer core materials to achieve a dramatic decrease in transformer core operating losses.
Amorphous metals are principally characterized by a virtual absence of a periodic repeating structure on the atomic level, i.e., the crystal lattice, which is a hallmark of their crystalline metallic counterparts. The non-crystalline amorphous structure is produced by rapidly cooling a molten alloy of appropriate composition such as those described by Chen et al., in U.S. Pat. No. 3,856,513, herein incorporated by reference. Due to the rapid cooling rates, the alloy does not form in the crystalline state, but assumes a metastable non-crystalline structure representative of the liquid phase from which it was formed. Due to the absence of crystalline atomic structure amorphous alloys are frequently referred to as "glassy" alloys.
Due to the nature of the manufacturing process, an amorphous ferromagnetic strip suitable for winding a distribution transformer core, for example, is extremely thin, nominally one mil versus 7-12 mils for grain oriented silicon steel. Moreover, such amorphous ferromagnetic strips are quite brittle and thus easily fractured. Consequently, the fabrication of wound amorphous metal cores presents unique problems of handling the very thin strips throughout the various manufacturing steps of winding the core, cutting and rearranging the core laminations into a desired joint pattern, shaping and annealing the core, and finally lacing the core through the window of a preformed transformer coil, which involves first opening and then reclosing the joints in the core. Of particular importance is the lacing step which must be effected with great care to avoid permanently deforming the core from its annealed configuration after the core has been laced into the coil window. That is, if the core is not exactly returned to its annealed shape, stresses are introduced during the lacing procedure. Consequently, if there are significant stresses remaining after lacing, the potential low core loss characteristic offered by the amorphous metal core material is not achieved. Since amorphous metal laminations are quite weak and have little resiliency, they are readily disoriented during the lacing step, resulting in permanent core deformation if not corrected. In addition to this concern, there is also the obvious concern that the lacing step be carried out with sufficient care such as to avoid fracturing the brittle amphorous metal laminations.
It is accordingly an object of the present invention to provide an improved wound amorphous metal transformer core and coil assembly.
An additional object is to provide a wound amorphous metal core and coil assembly of the above character wherein the potential low core loss characteristic thereof is preserved during the transformer manufacturing process.
A further object is to provide a wound transformer core of the above character, wherein the amorphous metal laminations thereof are restrained against disorientation during the lacing step of assembling the core with a winding coil.
Another object is to provide a wound transformer core of the above-noted character wherein the amorphous metal laminations thereof are protected against breakage through the transformer manufacturing process.
A still further object is to provide a wound amorphous metal transformer core which is efficient in design, economical to manufacture and reliable over a long service life.
Another object of the invention is to provide an improved method for manufacturing a transformer core and coil assembly of the above-noted character.
Other objects of the invention will in part be obvious and in part appear hereinafter.